headphone jack

Following time backward, for portable music we’ve had iPods, CDs, and cassette tapes which we played using small Walkmans around the size of a cigarette box. And for a brief time before that, in the 1960s and 1970s, we had 8-track tapes. These were magnetic tapes housed in cases around the size of a large slice of bread. Car dashboards housed players, and they also came in a carry-around format like the one [Todd Harrison] recently bought at a Hamfest for $5 and made more portable by machining clips for a strap and adding a headphone jack.

But before hacking it, he wanted to try it out. Luckily his sister had hung onto her old tapes and after plugging it in and sliding in a tape, it worked! Opening it up he found that the contacts for the batteries were rusted but the mechanical components and electronics inside were very clean. Though he did add glue to a crack in the plastic read-head support, cleaned out some grease, did some lubricating, and cleaned the contacts in the volume control’s potentiometer. Check out his teardown video below for those details or if you just want to see how it all works.

Then came making it portable so that he could embarrass his kids by carrying it around the mall. The shoulder strap didn’t come with it, so he machined some clips out of steel and snapped on a strap. It didn’t have a headphone jack and he didn’t want to embarrass his kids too much, so he added one. You can see that hack in the second video below, including how his repurposed jack automatically disconnects the speaker when the headphone plug is inserted. Personally, we think he looks pretty spiffy carrying it around wearing his Hackaday T-shirt.

The iPhone 7 features a barometric vent, which sits exactly where the headphone jack lived in the iPhone 6. The vent helps the barometric pressure sensor obtain an accurate reading while keeping the phone water proof. [Scotty] wasn’t worried about waterproofing, as he was cutting a hole through the case. The vent was out, replaced with a carefully modified headphone jack.

The next step was convincing the phone to play analog signals. For this, [Scotty] used parts from Apple’s own headphone adapter. The hard part was making all of this work and keeping the lightning port available. The key was a digital switch chip. Here’s how the circuit works:

When no headphone is plugged in, data is routed from the iPhone’s main board to the lightning port. When headphones are plugged in, the data lines are switched to the headphone adapter. Unfortunately, this means the phone can’t play music and charge at the same time — that is something for version 2.0.

The real journey in this video is watching [Scotty] work to fit all these parts inside an iPhone case. The design moved from a breadboard through several iterations of prototype printed circuit boards. The final product is built using a flexible PCB – the amber-colored Kapton and copper sandwiches that can be found in every mobile device these days.